It’s taken the musical “Cats” nearly 40 years to make its way from the stage to the big screen. Now we know why.

Just as there are some novels that defy dramatization, so there are stage productions that derive their power from the interaction of audience and performer, that work precisely because the viewer realizes that all the magic unfolding in front of him/her is being created by real people in real time.

Tom Hooper’s movie version, on the other hand, has been so digitally diddled with that we can’t be sure that anything we’re seeing — from the settings to the performers’ faces — is even remotely real. Characters do impossible flips in the air, cockroaches march in formation…it’s all so artificial that the film might as well have been done as pure animation (actually that was the plan, back in the ’90s).

That said, the movie “Cats” isn’t a total wipeout. The score (the tunes are by Andrew Lloyd Webber, the lyrics derived from T.S. Eliot’s book of poems Old Possum’s Book of Practical Cats) remains humworthy and at least a couple of the performers manage to transcend their hairy makeup (all too often they look like werewolves from a ’60s Hammer film) and establish an emotional connection with the audience.

A big problem is that “Cats” lacks a real story. On stage this wasn’t a deal breaker…the show was a musical revue with different “cats” taking center stage to sing and dance their signature numbers. What plot there was dealt with the approaching Jellicle Ball where one lucky feline will be chosen by the ancient Deuteronomy to be reincarnated into a new life (cats get nine of them, after all).

The screenplay by Lee Hall and Hooper centers on Victoria (ballerina Francesca Hayward, who seems capable of expressing only a quizzical attitude), abandoned by her owner in a dirty alley and adopted into the Jellicle tribe. Her guide and guardian is Munkstrap (Robbie Fairchild), who introduces her to various other characters and the rundown corner of London they call home.

Think about it: A reunion of old coworkers and their beloved characters, awesome scenery in the south of France, and a never-ending stream of famous-face cameos — Rebel Wilson, Jon Hamm, Joan Collins, Chris Colfer, Lily Cole, Jerry Hall, Lulu (yes, the “To Sir With Love” singer), Graham Norton, Gwendoline Christie, Perez Hilton, Stella McCarthy and more skinny supermodels than the brain can process — that turns the movie into a celebrity version of Where’s Waldo.

If only some of the fun had ended up on the screen.

Fans of the old “Ab-Fab” TV show will be bitterly disappointed. Newcomers will wonder why anybody bothered.

It’s enough to make you look back fondly on the “Sex and the City” movies.

The long-running ’90s Brit sitcom featured Jennifer Saunders (who scripted the series and this movie) as Edina Monsoon, a hoplessly inept p.r. maven to London’s fashion industry, and and Joanna Lumley as her running buddy Patsy Stone, an aging former model who can rarely think past where her next alcohol/pharmaceutical fix is coming from.

It was a savage comedy about a couple of reprehensible people.

Eddie and Patsy are still reprehensible, but the charm has worn very, very thin.